It will last a long time.
The Bypass, sure you can use one, but may be overkill, but not a bad way to go as long as it's installed properly.
The rx:
what? it's a diesel.
They are always nasty inside
but they don't get like gasoline engines
unless something wierd happened.
Do a flush or add some highly detergent adds in there, and or just use a very good oil that keeps things clean as possible, and I think you'll be fine.
I would take a sample 5-7K miles until theres a trend and then maybe push it out to a higher milage.
the bypass greatest advantage is the soot
the length of life it gives could vary
but I wouldn't doubt that on a good oil that you would be looking at very high milages.